Meteorology in the Middle Ages

PART IThermally driven Coastal Flows

Modern texts on thermally driven coastal winds

(met.no)

Sea breeze Land breeze

A: Sea breeze, B: Land breeze

Wikipedia:

NB: Sloping land

Land breeze (Wikipedia)

Land breezesAt night, the land cools off quicker than the ocean due to differences in

their specific heat values, which forces the dying of the daytime sea

breeze. If the land cools below that of the adjacent sea surface temperature, the pressure over the water will be

lower than that of the land, setting up a land breeze as long as the environmental surface wind pattern is not strong enough to oppose it. If there is sufficient moisture and instability available, the land breeze can cause showers or even thunderstorms, over the water. Overnight

thunderstorm development offshore can be a good predictor for the activity on land the following day, as long as there are no expected changes to the

weather pattern over the following 12-24 hours. The land breeze will die once the land warms up again the next morning.

Egils saga

Snorri Sturluson(?)A.D. 1220 (?)

Snorri SturlusonA wealthy politician and an outstanding scholar in Iceland. Assassinated at his home in Iceland upon request from Håkon the foul, king of Norway on the 23rd of September 1241

Snorri Sturluson

Egill Skallagrímsson

Magnus with naked legs,king of Norway

Þóra Magnúsdóttir

Jón Loftsson

Ólafur, Haraldur, Eiríkur,Hákon, Hálfdán, kingsof Norway

6 generations

Familyrelations

Egill Skallagrímsson (10th Century)

A very good poet, mercenary in England and Continental Europe, greedy, strong and clever

Egil´s father and grandfather fled from Norway to Iceland around 880 AD.

Egill claimed an inheritance in Norway on behalf of his wife

Eirik bloodaxe, king of Norway(10th century)

Greedy, strong, ill-tempered and maybe not excessively clever

Prevents Egill from collecting the money

Egil´s saga (English transl. W. C. Green, 1893 )

The weather was calm, a fell-wind blew by night, a sea breeze by day. One evening Egil sailed out to sea, but the fishermen were then rowing in to land, those, to wit, who had been set as spies on Egil's movements. They had this to tell, that Egil had put out and sailed to sea, and was gone. This news they carried to Bergonund. And when he knew these tidings, then he sent away all those men that he had had before for protection. Thereafter he rowed in to Alrekstead, and bade Frodi to his house, for he had a great ale-drinking there. Frodi went with him, taking some men. They were feasted well there, and they made merry, with no fear of danger…. There too was no lack of drink.

fell-wind = fjallvindr = katabatic wind

Gravity forceHL

Land breeze

Katabatic flow

Pressure gradient force

There are in fact two forces at stake

Who is right, Snorri and Egill or the spirit of the modern textbooks?

We simulate the thermally driven winds

Model: MM5, Dx=3km, starting from rest with clear skies

N-IcelandSurface winds late summer night

Ágústsson & Ólafsson, 2008

Flat IcelandSurface winds late summer night

Surface winds in December

Flat

”True” topography

Ágústsson & Ólafsson, 2008

South-Iceland Lowlands: No winds from land

A mountainous region in N-Iceland. Strong flow to the sea

How did Snorri know that the land breeze was katabatic flow?

Snorri grew up here

Egil´s saga (English transl. W. C. Green, 1893 )

The weather was calm, a fell-wind blew by night, a sea breeze by day. One evening Egil sailed out to sea, but the fishermen were then rowing in to land, those, to wit, who had been set as spies on Egil's movements. They had this to tell, that Egil had put out and sailed to sea, and was gone. This news they carried to Bergonund. And when he knew these tidings, then he sent away all those men that he had had before for protection. Thereafter he rowed in to Alrekstead, and bade Frodi to his house, for he had a great ale-drinking there. Frodi went with him, taking some men. They were feasted well there, and they made merry, with no fear of danger…. There too was no lack of drink.

Where is the katabatic flow going to bring Egill?

They thought that the katabatic wind would bring Egill far away – to England or Iceland!

”Egil sailed out to sea for the night, as was written above. And when morning came the wind fell and there was a calm. They then lay drifting, letting the ship ride free for some nights. But when a sea-breeze came on, Egil said to his shipmen, ’We will now sail to land,…”

Egill returned and killed all the king´s men, Egill raises a curse-pole and sets the curse that Eirikur blood-axe will lose his kingdom.

He did very soon thereafter

First conclusions

These men knew about thermally driven coastal winds, their knowledge was solid on nighttime flows, more solid than some modern textbooks

The alleged land-breeze in Iceland (and most likely Norway too) is not land-breeze, but katabatic wind

Do not rely on people that are ignorent in meteorology if you want to keep your kingdom

Meteorology in the Middle Ages

PART IIA downslope windstorm

Laxdæla saga

Ólafur Þórðarson (?)A.D. 1255 (?)

A ship sinks

The drowning of Þorsteinn Surtur – Höskuldur buys Hrappsstaðir farm

Höskuldur Dala-Kollsson

Mýrkjartan, king of Ireland

Ólafur Pá Höskuldsson

Ólafur Tryggvason, king of Norway

Kjartan Ólafsson

Ingibjörg, sister of Ólafur Tryggvason, king of Norway

Hrútur

Gunnhildur, wife of Eirik Bloðöx, king of Norway

Egill Skallagrímsson

Snorri Sturluson

Kings of Scotland and the Hebrides

Myrkjartan, king of Ireland(around 970 AD)

Melkorka, doughter of Myrkjartan

Ólafur ”Pá” Höskuldsson

Melkorka

Ólafur

    

Myrkjartan, king of Ireland

Melkorka Mýrkjartansdóttir. (910)  

Höskuldur Dala-Kollsson (910)  

        Ólafur "pá" Höskuldsson

0930

Þorbjörg "digra" Ólafsdóttir

0960

Kjartan Ásgeirsson 1000

Þorvaldur Kjartansson

1055

Þórður Þorvaldsson 1075 - 1143

Snorri Þórðarson 1125 - 1194

Þorvaldur Snorrason 1160 - 1228

Einar Þorvaldsson 1227 - 1286

Ónefnd Einarsdóttir 1250

Eiríkur Sveinbjarnarson

1277 - 1342

Einar Eiríksson 1320 - 1382

Björn "Jórsalafari" Einarsson

1350 - 1415

Kristín Björnsdóttir 1374 - 1468

Björn "ríki" Þorleifsson

1408 - 1467

Þorleifur Björnsson 1430 - 1486

Helga Þorleifsdóttir 1470

Kristín Eyjólfsdóttir 1515

Vilborg Gísladóttir 1555

Erlendur Þorvarðsson 1585

Þorvarður Erlendsson 1620 - 1690

Einar Þorvarðarson 1650 - 1703

Þorvarður Einarsson 1691 - 1769

Agatha Þorvarðardóttir

1762 - 1788

Kristrún Guðmundsdóttir

1787 - 1870

Gísli Guðmundsson 1817 - 1899

Kristrún Gísladóttir 1854 - 1942

Ólafur Einarsson 1888 - 1980

Ólafur Einar Ólafsson 1928 - 1974

Haraldur Ólafsson

Eydís Lilja Haraldsdóttir

1965

1999 -

Eydís Lilja Haraldsdóttir (b.1999)Melkorka Myrkjartansdóttir (~910)

Thorstein's daughter, and Hild, her daughter, who was three years old, went with them too. Thorstein fell in with a high south-westerly gale, and they sailed up towards the roosts, and into that roost which is called Coal-chest-Roost,which is the biggest of the currents in Broadfirth. They made little way sailing, chiefly because the tide was ebbing, and the wind was not

favourable, the weather being squally, with high wind when the squalls broke over, but with little wind between whiles.

1880, English transl. Muriel A. C. Press,

the ebbing of the sea, but the breeze was not friendly to them; for the weather was showery and the wind was strong when it grew clear, but blew little between-whiles.

1903, English v.2 transl. Robert Proctor

Two versions/possibilities

• Convective precipitation associated with a temporary increase in wind speed

• Strong winds during a clearing: A downslope windstorm associated with a (weak) front in stably stratified southerly flow

Laxdæla Ch.18Icelandic (Old Norse):Þorsteinn tók útsynning hvassan. Sigla þeir inn að straumum í þann straum er hét Kolkistustraumur. Sá er í mesta lagi þeirra strauma er á Breiðafirði eru. Þeim tekst siglingin ógreitt. Heldur það mest til þess að þá var komið

útfall sjávar en byrinn ekki vinveittur því að skúraveður var á og var hvasst veðrið þá er rauf en vindlítið þess í milli. Þórarinn stýrði og hafði aktaumana um herðar sér því að þröngt var á skipinu.

New-Norwegian (Nynorsk):Osk Torsteinsdotter og Hild Helgesdotter, som var berre 3 vintrar gamall. Dei fekk ein kvass sudvest og siglde etter straumom inn i Kolkistestraumen, ein av dei sterkaste straumom i Breidafjorden. Der vart det ugreidt med

siglingi deira, av di at sjøen fall og vinden ikkje var god; for det var skurver, kvast naar det reiv i, men mest stilt dessimillom. Torarin styrde og hadde brasen um akslerne sine, av di det var trongt paa skipe

Two possibilities

• Convective precipitation associated with a temporary increase in wind speed

• Strong winds during a clearing: A downslope windstorm associated with a (weak) front in stably stratified southerly flow

And the MM5 is restarted:

Wind speed forecast, valid 6 June 2008 at 15 UTC dx=3km

www.belgingur.is

Mountain crest

Strong downslope flow

MS Edda sank in a downslope windstorm at the South Coast of Breidafjörður in 1953

Meteorology in the Middle Ages

PART IllThe early discoveries of the Bergen Cyclone Model and

America

Then the king and Gunnhild bade Olaf farewell. Then Olaf and his men got on board, and sailed out to sea. They came in for unfavourable weather through the summer, had fogs plentiful, and little wind, and what there was was unfavourable; and wide about the main they drifted, and on most on board fell "sea- bewilderment." But at last the fog lifted over head; and the wind rose, and they put up sail. Then they began to discuss in which direction Ireland was to be sought; and they did not agree on that. Orn said one thing, and most of the men went against him, and said that Orn was all bewildered: they should rule who were the greater in number. Then Olaf was asked to decide. He said, "I think we should follow the counsel of the wisest; for the counsels of foolish men I think will be of all the worse service for us in the greater number they gather together."

From Laxdæla. Ólafur Pá is on his way to his grandfather, the king of Ireland:

Where did Örn get his knowledge from?What was there to do when you were lost at sea?Is democracy useless?

The King’s Mirror (Konungsskuggsjá)Written around 1240

The King’s mirror has a chapteron meteorology:

Rain is associated with southeasterly winds

Fog is associated with southerly winds

Rainshowers are associated with southwesterly winds

See Páll Bergþórsson; The Wineland Millenium, 2000

This is the Bergen Cyclone Model!

Can we use the wisdom of the King´s Mirror to navigate?

The navigators could- tell the time of the day- estimate the latitude (if not overcast)(- determine the wind direction from the clouds)

1324 1

32

Using the rules of the King’s Mirror, it becomes apparently quite easy tonavigate across the ocean

Experiment:4 ships depart from Norway towards Iceland on 4 different days in June - they all arrive safely in less than 5 days

13 24 13 2

?

FLOW OVER MOUNTAINS

{ Nh/U } > { Nh/U } C

{ Nh/U } C = (mountain shape,∂/∂ z (U,N),...) ≈ 1.5

=> Blocked flows

BLOCKING

WAKESLOWSLOW

FAST

Dense Air

H L L

N = Brunt-Vaisala frequency (stability), U = Wind speed; h = Mountain height

Ólafsson & Ágústsson, Meteorol. Atm. Phys., 2009

Surface winds almost perpendicular to the isobars

Greenland in easterly flow

Ro=U/fL

Nh/U0.1 101

0.1

1

10

T

Red=speed up Green=slow down

The mountain wind forecasting diagram

Ólafsson, 2004

13 24 13 2

Bjarni Herjólfssonapprox. 999 A.D.

FOG

The first European settlements in N-America were a direct result ofBjarni Herjólfsson’s lack of knowledge of mountain meteorology

Bjarni Herjólfsson set off for Greenland. His ship sailed into fog and barrier winds blowing from the NE to the southeast of Greenland. Bjarni turned too far to the south,missed Greenland and ended up in Wineland (America).

Bottom line:

They knew more than we think they

did

Laxdæla:

The king answered, "This is clearly seen in this Olaf, that he is a highborn man, whether he be a kinsman of mine or not, as well as this, that of all men he speaks the best of Irish.”

Bottom line II: Wise and highborn men speak Irish

Thank you

The king answered, "This is clearly seen in this Olaf, that he is a highborn man, whether he be a kinsman of mine or not, as well as this, that of all men he speaks the best of Irish."

Then they rode so near to the ship, that each could hear what the other said. The king asked who was the master of the ship. Olaf told his name, and asked

who was the valiant-looking knight with whom he then was talking.

He answered, "I am called Myrkjartan."

Olaf asked, "Are you then a king of the Irish?"

He said he was.

Egils saga (1893, English transl. W. C. Green )

The weather was calm, a fell-wind blew by night, a sea breeze by day. One evening Egil sailed out to sea, but the fishermen were then rowing in to land, those, to wit, who had been set as spies on Egil's movements. They had this to tell, that Egil had put out and sailed to sea, and was gone. This news they carried to Bergonund. And when he knew these tidings, then he sent away all those men that he had had before for protection. Thereafter he rowed in to Alrekstead, and bade Frodi to his house, for he had a great ale-drinking there. Frodi went with him, taking some men. They were feasted well there, and they made merry, with no fear of danger. Rognvald, the king's son, had a pinnace, rowed by six men on either side, painted all above the sea line. He had with him ten or twelve who constantly followed him; and when Frodi had left home, then Rognvald took the pinnace and they rowed out to Herdla twelve in number. A large farm of the king's was there, whereof the manager was named Skegg-Thorir. Rognvald in his childhood had been fostered there. Thorir received the king's son joyfully. There too was no lack of drink.

Sea and land breezes occur along the coastal regions of oceans or large lakes in the absence of a strong large-scale wind system during periods of strong daytime heating or nighttime cooling. Those who live within 10 to 20 km (6 to 12 miles) of the coastline often experience the cooler 19- to 37-km-per-hour (12- to 23-mile-per-hour) winds of the sea breeze on a sunny afternoon only to find it turn into a sultry land breeze late at night. One of the features of the sea and land breeze is a region of low-level air convergence in the termination region of the surface flow. Such convergence often induces local upward motions and cloud formations. Thus, in sea and land breeze regions, it is not uncommon to see clouds lying off the coast at night; these clouds are then dissipated by the daytime sea breeze, which forms new clouds, perhaps with showers occurring over land in the afternoon.

http://www.britannica.com/EBchecked/topic/121560/climate/53291/Local-winds#ref293131

The drowning of Þorsteinn Surtur – Höskuldur buys Hrappsstaðir farm

Höskuldur Dala-Kollsson

Mýrkjartan, king of Ireland

Ólafur Pá Höskuldsson

Ólafur Tryggvason, king of Norway

Kjartan Ólafsson

Ingibjörg, sister of Ólafur Tryggvason, king of Norway

Hrútur

Gunnhildur, wife of Eirik Bloðöx, king of Norway

Snorri Sturluson

These men knew about katabatic winds, sea breeze, downslope windstorms – and the Bergen School Cyclone Model

Solgangsbris (land- og sjøbris): På varme sommerdager med mye sol blir landjorda varmet opp. Det dannes lavtrykk over land. Lufta stiger og brer seg mot sidene i høyere luftlag, mens luft siger inn fra sjøen i lavere luftlag (sjøbris). Om natta skjer det motsatte: I klarvær avkjøles landjorda mye og det dannes et svakt høytrykk over land med tilhørende lavtrykk over sjøen (landbris). Monsun er et annet fenomen med samme årsak som solgangsbris. Men monsunen skifter retning bare 2 ganger i året. Mer om monsun.Sjøbris:Sjøluft blir dratt inn mot lavtrykket, dvs. inn mot land. Effekten kan merkes fra tidlig formiddag, men er som regel sterkest et stykke ut på ettermiddagen. Langs det meste av Norskekysten kan vindstyrken komme opp i ca frisk bris 8-10m/s. I tillegg kan det være andre årsaker til at vindstyrken blir høyere eller lavere. Sjøbrisen kan av og til merkes flere mil inn over land, men med mindre styrke enn på kysten. Vindretningen dreier etter hvert som sola passerer over horisonten, derav navnet solgangsbris. Først blåser det rett på kysten, senere parallelt med kysten. Retningen bestemmes i hovedsak av trykk-kraften (lavtrykksplasseringen) og Coriolis-kraften, og varierer langs kysten. Lurer du på hvilken retning det er i ditt nærområde? Se oppgaven nederst på siden.   "Havgula" er et annet navn på sjøbris som særlig er brukt på Vestlandet. Landbris: Om natta ligger lavtrykket over sjøen og lufta siver ut fra land. Landbrisen er som regel svak, men det kan blåse friskt enkelte steder. Et stykke fra land kan man også om natta merke at Coriolis-krafta dreier vinden mot høyre. http://retro.met.no/met/met_lex/q_u/solgangsbris.html

Laxdæla Ch.18Þorsteinn tók útsynning hvassan. Sigla þeir inn að straumum í þann straum er hét Kolkistustraumur. Sá er í mesta lagi þeirra strauma er á Breiðafirði eru. Þeim tekst siglingin ógreitt. Heldur það mest til þess að þá var komið

útfall sjávar en byrinn ekki vinveittur því að skúraveður var á og var hvasst veðrið þá er rauf en vindlítið þess í milli. Þórarinn stýrði og hafði aktaumana um herðar sér því að þröngt var á skipinu.

Osk Torsteinsdotter og Hild Helgesdotter, som var berre 3 vintrar gamall. Dei fekk ein kvass sudvest og siglde etter straumom inn i Kolkistestraumen, ein av dei sterkaste straumom i Breidafjorden. Der vart det ugreidt med

siglingi deira, av di at sjøen fall og vinden ikkje var god; for det var skurver, kvast naar det reiv i, men mest stilt dessimillom. Torarin styrde og hadde brasen um akslerne sine, av di det var trongt paa skipe

Egils saga Ch.59Veður voru vindlítil, fjallvindur um nætur, en hafgola um daga. Eitt kveld sigldu þeir Egill út á haf, en fiskimenn reru þá inn til

lands, þeir er til njósnar höfðu settir verið um farar þeirra Egils. Kunnu þeir það að segja, að Egill hafði út látið og á haf siglt og hann var á brottu; létu þessa njósn

koma til Berg-Önundar. Og er hann vissi þessi tíðindi, hann sendi þá frá sér menn þá er hann hafði áður

haft þar til varúðar. Reri hann þá inn til Álreksstaða og bauð Fróða til sín, því að Berg-Önundur átti öl mikið heima að sín; Fróði fór með honum og hafði með

sér nokkura menn; tóku þeir þar veislu góða og höfðu gleði mikla; var þar þá allt óttalaust.

Rögnvaldur konungsson átti karfa einn, reru sex menn á borð; hann var steindur allur fyrir ofan sjó; hann hafði með sér menn tíu eða tólf, þá er honum fylgdu einart.

Og er Fróði var heiman farinn, þá tók Rögnvaldur karfann, og reru þeir út til Herðlu tólf saman; þar var konungsbú mikið, og réð sá maður fyrir, er hét Skegg-

Þórir; þar hafði Rögnvaldur verið á fóstri í barnæsku. Tók Þórir feginsamlega við konungssyni; skorti þar og eigi drykk mikinn.

The king answered, "This is clearly seen in this Olaf, that he is a highborn man, whether he be a kinsman of mine or not, as well as this, that of all men he speaks the best of Irish."

Then they rode so near to the ship, that each could hear what the other said. The king asked who was the master of the ship. Olaf told his name, and asked

who was the valiant-looking knight with whom he then was talking.

He answered, "I am called Myrkjartan."

Olaf asked, "Are you then a king of the Irish?"

He said he was.

The king answered, "This is clearly seen in this Olaf, that he is a highborn man, whether he be a kinsman of mine or not, as well as this, that of all men he speaks the best of Irish."

He began his speech thus: "You all know that last autumn there came hither a man who is the son of my daughter, and highborn also on his father's side; and it seems to me that Olaf is a man of such prowess and courage that here such men are not to be found. Now I offer him my kingdom after my day is done, for Olaf is much more suitable for a ruler than my own sons.”

Olaf thanked him for this offer with many graceful and fair words, and said he would not run the risk as to how his sons might behave when Myrkjartan was no more; said it was better to gain swift honour than lasting shame; and added that he wished to go to Norway when ships could safely journey from land to land, and that his mother would have little delight in life if he did not return to her.